gear ratio questions

hey all. i'm going to be picking up a singlespeed in two weeks and i noticed the gearing on the one i want is really low and i want to change it. i almost exclusively do city riding and commuting and don't really have many crazy hills anywhere in my city. what ratio is best for this kind of riding? i also want to get pretty good speed while riding the flats. will i have to compromise for this and be forced to grind up even the tiniest hill? all your help is appreciated.

On my 26" wheeled townie/grocery getter I've played around and run the following gears: 44x16, 44x18, 42x16, 42x18. The 42x18 was way too low for the flats. I liked 44x16 a lot for making time. 44x18 is on there now and works good for the times I have the bike loaded down with groceries and have to climb the steep hill back to my house. I don't notice much of a loss of the top end (compared to 44x16) when cruising. FWIW, the bike is a pig too, even unloaded.

On my 700c fixed gear I run 44x17 or 42x17 and it works pretty good. Lots of hills around my way.